Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations (BSs) each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In particular, each coverage area may operate on one or more carriers each defining a respective frequency bandwidth of coverage. In turn, each base station (BS) may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a BS and may thereby communicate via the BS with various remote network entities or with other UEs served by the BS.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol (radio access technology), with communications from the BSs to UEs defining a downlink or forward link and communications from the UEs to the BSs defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with the air interface protocol, each coverage area provided by the BS may operate on one or more radio frequency channels each spanning a range of frequency spectrum, and the air interface may be divided over time into a continuum of transmission time units, such as frames, subframes, timeslots, symbol durations, and the like, in which communications may pass on a downlink from the BS to the UEs and on an uplink from the UEs to the BS using a designated modulated and encoding scheme. Such carriers may be frequency division duplex (FDD), in which the downlink and uplink channels are defined as separate respective ranges of frequency, or time division duplex (TDD), in which the downlink and uplink channels are defined on a common range of frequency but are distinguished from each other through time division multiplexing. Further, the downlink and uplink channels may then define various sub-channels for carrying particular communications, such a control signaling and bearer data (e.g., user communications) between the BS and served UEs.
As UEs enter into coverage of the BS, the BS may become configured with connections to serve those UEs. For instance, for each such UE entering coverage on a particular carrier, the BS may engage in signaling with the network infrastructure to establish a bearer connection for carrying data between a gateway system and the BS, and the BS may work with the UE to establish a radio-link-layer connection for carrying data over the air between the BS and the UE on the carrier. Once so configured, the BS may then serve the UEs. For instance, when data arrives over the transport network for transmission to a UE, the gateway system may transmit the data over the UE's bearer connection to the BS, and the BS may then transmit the data over the UE's radio-link-layer connection to the UE.
In such a wireless communication system, the BS may manage the transmission of data on the downlink and uplink in the defined transmission time units and in particular resources, such as particular subcarriers defined in those transmission time units. For instance, as the BS receives data destined to particular UEs, the BS may schedule downlink transmission of that data to occur in particular transmission time units and may transmit the data over the air to the UEs in the scheduled transmission time units. Similarly, as UEs have data to send to the BS, the UEs may send scheduling requests to the BS, the BS may then schedule uplink transmission of that data to occur in particular transmission time units, and the UEs may then transmit the data over the air to the BS in the scheduled transmission time units.
Each carrier on which a BS provides service will have a limited supply of resources on which to transmit data to served UEs. For instance, each carrier will have a limited frequency bandwidth. Further, depending on the air interface protocol, only certain portions of a carrier's frequency bandwidth and/or certain segments of time may be designated for use to carry data to served UEs. Other resource limitations may be possible as well.
In order to help manage data transmission resources given these limitations, the BS may be configured to impose a per-UE data transmission rate cap. When applying such a rate cap on a carrier, as the BS receives data packets for transmission to a UE on the carrier, the BS may limit its rate of transmission of that data to be no greater than the rate cap and may buffer any excess data (i.e., data exceeding the rate cap) destined to the UE. For this purpose, the BS may establish and maintain in physical data storage a respective data buffer for each such UE, with each such data buffer being statically or dynamically sized. Further, the BS may be configured to apply a buffer timeout process according to which the BS drops a data packet from the buffer (e.g., deletes or reroutes the packet) in response to the data packet being in the buffer for a timeout period. By dropping data packets in this manner, the BS can manage the data load of a respective data buffer, so as to avoid overloading that data buffer for example.
In a further aspect, BSs in a cellular wireless network can be physically arranged in various ways. For instance, BSs may be co-located with each other by having their antenna structures at largely the same geographic location (within a defined tolerance, for instance). By way of example, a single cell site could be arranged to define two BSs with separate antenna structures on a common antenna tower or other base structure. And in another example, a single physical BS that provides service separately on first and second carriers could be considered to define the two separate BSs, one operating on the first carrier and the other operating on the second carrier. Alternatively, BSs in a cellular wireless network can be distributed at some distance from each other. In particular, the antenna structure of a given BS may be located at a geographic location that is at some non-zero distance from the antenna structure of another BS.
With these arrangements, the BSs of a wireless service provider's network would ideally provide seamless coverage throughout a market area, so that UEs being served by the system could move from coverage area to coverage area without losing connectivity. In practice, however, it may not be possible to operate a sufficient number of BSs or to position the BSs in locations necessary to provide seamless coverage. As a result, there may be holes in coverage.
One way to help to resolve this problem is to operate a relay node (RN) that effectively extends the range of a BS's coverage area so as to partially or completely fill a coverage hole. Such an RN may be configured with a wireless backhaul interface for communicating with and being served by the BS, referred to as a “donor BS,” and may also be configured with a wireless access interface for communicating with and serving one or more end-user UEs, such as a cell phone, wirelessly equipped computer, tablet, and/or other device that is not set to provide wireless backhaul connectivity. For example, the RN could include a relay base station (relay-BS) that serves end-user UEs and could also include a relay-UE that is served by the donor BS and thus provides wireless backhaul connectivity for the relay-BS. In practice, the relay-BS and relay-UE could be integrated together as a single RN device or could be provided as separate devices communicatively linked together.
In this arrangement, the BS is considered to be a donor BS, in that the BS provides coverage to the relay-UE, and the relay-B S then provides coverage to one or more end-user UEs. Also, the wireless communication link between the donor BS and the relay-UE is considered to be a “relay backhaul link,” and the wireless communication link between the relay-BS and UEs served by the relay-BS is considered to be a “relay access link.” Further, to the extent the donor BS itself also serves end-user UEs, the wireless communication link between the donor BS and those UEs is considered to be a “donor access link.”
Given these arrangements, a donor BS may receive from the network data packets destined to the relay-UE and perhaps ultimately destined to one or more of the end-user UEs being served by the relay-BS (referred to herein as RN-served UEs). In particular, a data packet may include (e.g., in a header of the data packet) a network address of the relay-UE and/or of the RN-served UE destined to receive the data packet. In this way, a donor BS and/or other network entity could read the network address from the data packet and based on that network address may determine that the data packet is destined to the relay-UE and perhaps ultimately to the RN-served UE. As such, when a data packet arrives over the transport network for transmission to the relay-UE or to an RN-served UE, the gateway system may transmit the data packet to the donor BS over the relay-UE's or the RN-served UE's bearer connection. Then, the donor BS may transmit the data packet over a wireless backhaul connection to the relay-UE. Moreover, the relay-BS may receive the data packet from the relay-UE and may then transmit the data packet to the RN-served UE if that data packet is destined to that RN-served UE.
In practice, data packets destined to RN-served UEs may include various types of communications. Generally, such communications could be categorized into control signaling traffic and bearer data communications. In particular, control signaling traffic may help manage service of RN-served UEs, and could thus include bearer setup signaling, tracking area update signaling, and/or handover signaling, among others. Whereas, a bearer data communication may encompass user data, such as voice data, text data, video data, and/or web data, among others.